The present invention relates to venting of gasses from fluids, and in particular, venting of gasses from filter elements or filter media used in water treatment devices.
In particular, this invention relates to a multi-stage filter cartridge that incorporates a fluid flow diverter to vent air from an interface between stages of the filter cartridge.
Major categories of domestic point-of-use (POU) systems include: a) plumbed-in or faucet-mounted systems that rely on the pressure of the water supply as the driving force for filtration, and b) non-plumbed pour-through or batch systems that rely on gravity to force water from an upper influent water chamber, through a filtering means and down to a lower effluent water chamber.
Typical POU systems known in the art employ various combinations of purification agents that remove contaminants by chemical or physical means. These purification agents may be present in forms such as, but not limited to porous, non-porous, granular, fibrous, filamentous or particulate. Examples of these purification agents include zeolites, ion exchange resins, activated carbons and mechanical filtration medias. Such agents remove contaminants from water through processes such as adsorption, chemical reaction and size exclusion. The use of such purification agents can result in air entrapment within filter cartridges because some agents are hydrophilic (xe2x80x9cwater-lovingxe2x80x9d) and therefore air-impervious. Since the pressure available to a gravity driven filtration system is typically 1.0 pounds per square inch (PSI) or less, air trapped within the filter cartridge is unlikely to be forced out with the effluent water. But rather, because of its buoyancy, air tries to move upward through the cartridge. However, when the air encounters a wetted purification agent with a hydrophilic nature, it becomes trapped due to surface tension at the air/liquid interface.
A typical gravity driven system which has an upper reservoir, a filter, and a lower filtered water collection chamber is described in U.S. Pat. Nos. 4,895,648 and 4,969,996, both to Hankammer, the disclosures of which are incorporated by reference herein.
Thus, one problem to be overcome in designing filter cartridges for gravity-driven POU systems is the venting of air from the cartridge. During normal use of such cartridges, air is often trapped inside. This is particularly true for multi-stage filters where several purification agents of differing hydrophilicities are used. This trapped air can cause many problems including preventing the filter cartridge from functioning at maximum flow rate, causing channeling of the filtering water, or even result in filter lock-up where no water is flowing at all. When such a filter is new, air originally within the filter before use must be vented, and any time water flow through the filter cartridge is interrupted, accumulated air may need to be vented.
Examples of venting strategies are known in the art. Saito (U.S. Pat. No. 5,225,079) and Kawai (U.S. Pat. No. 4,772,390) both employ air-pervious, water-impervious membranes through which the trapped air is vented while at the same time preventing filter leakage. However, this strategy requires the relatively higher pressure of a plumbed-in or faucet-mounted filtration system to efficiently vent the trapped air in a reasonable amount of time. Hankammer (U.S. Pat. No. 4,895,648) teaches the use of a filter cover connected to a hollow tube that vents air from the top of the single stage or component filter. However, this method has three disadvantages: it only vents air that manages to rise to the top of the filter cartridge and cannot vent the air trapped near the bottom of the cartridge, the filter cover is external to the filter cartridge and thus can be inadvertently removed or lost by the user, and since this filter cover resides in the upper influent water chamber, water can enter the opening in the filter cover tube, block the air release ports at the top of the filter cartridge lid by surface tension, and cause filter lockup.
The present invention provides a means of venting air trapped at the bottom of the filter cartridge and unable to rise to the top, or which is internal to the filter cartridge. The structural configuration of the venting structure is such that it cannot be inadvertently blocked by the surface tension of water. The vent structure has utility in any apparatus wherein a gas is or becomes entrained or mixed with a fluid, and in particular where such gas may impede, slow or interfere with fluid flow, or where it is desirable to removes gases for any reason. In particular, a multi-stage filter having two or more filtration systems, arranged axially along the fluid flow path, results in an interface between stages which may generate, entrap or entrain air or gases within the fluid.
In particular, the vent structure is useful in systems having a pressure drop of 1 psi or less, such as those systems which filter a fluid by a pressure differential generated by gravity alone, or aided by a manual pressurization means. Pressure drop can be measured directly with a gauge, or can be calculated by measuring the vertical height of the water column across the structure to which the pressure drop applies.
As used herein the term xe2x80x9cfluid communicationxe2x80x9d means a path by which liquids or gases may move between two or more structures. The term xe2x80x9cliquid communicationxe2x80x9d means a path by which liquids may move between two or more structures. The term xe2x80x9cmulti-stagexe2x80x9d means two or more stages. The term xe2x80x9cpottedxe2x80x9d means fixing or sealing hollow fiber bundles to hold them in place and to provide a defined fluid flow pathway. Also as used herein, air and gases are used interchangeably, unless otherwise apparent from the context.